You know, they cant just "fix" it with the click of a button.
It takes ages to make Minecraft have better performance, not because of forge but because of Minecraft and java compilation.
Minecraft does not support multi-threading, which is a BIG issue as if you had a 4x CPU in your PC, well guess what: Minecraft will only use the power of one of the CPU. If Minecraft was multi-threaded, it would use the power of all 4 CPU and give you quite a big fps boost, probably around 4x the fps.
*something used to be here, removed now*
Note: im not trying t